<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

</head>

<body>
    <div id="app">
        <button id="btn" onclick="fn()">反选</button>
        <button id="btn" onclick="fn1()">全选</button>
        <button id="btn" onclick="fn2()">全不选</button>
        <ul>
            <li><input type="checkbox" checked class="select"></li>
            <li><input type="checkbox" class="select"></li>
            <li><input type="checkbox" checked class="select"></li>
            <li><input type="checkbox" class="select"></li>
            <li><input type="checkbox" class="select"></li>
        </ul>
    </div>
    <script src="../js/task6.js"></script>

</body>

</html>